Aop: 260

Title

Each AOP should be given a descriptive title that takes the form “MIE leading to AO”. For example, “Aromatase inhibition [MIE] leading to reproductive dysfunction [AO]” or “Thyroperoxidase inhibition [MIE] leading to decreased cognitive function [AO]”. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE. More help

CYP2E1 activation and formation of protein adducts leading to neurodegeneration

Short name
A short name should also be provided that succinctly summarises the information from the title. This name should not exceed 90 characters. More help
CYP2E1 activation and formation of protein adducts leading to neurodegeneration

Graphical Representation

A graphical summary of the AOP listing all the KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs should be provided. This is easily achieved using the standard box and arrow AOP diagram (see this page for example). The graphical summary is prepared and uploaded by the user (templates are available) and is often included as part of the proposal when AOP development projects are submitted to the OECD AOP Development Workplan. The graphical representation or AOP diagram provides a useful and concise overview of the KEs that are included in the AOP, and the sequence in which they are linked together. This can aid both the process of development, as well as review and use of the AOP (for more information please see page 19 of the Users' Handbook).If you already have a graphical representation of your AOP in electronic format, simple save it in a standard image format (e.g. jpeg, png) then click ‘Choose File’ under the “Graphical Representation” heading, which is part of the Summary of the AOP section, to select the file that you have just edited. Files must be in jpeg, jpg, gif, png, or bmp format. Click ‘Upload’ to upload the file. You should see the AOP page with the image displayed under the “Graphical Representation” heading. To remove a graphical representation file, click 'Remove' and then click 'OK.'  Your graphic should no longer be displayed on the AOP page. If you do not have a graphical representation of your AOP in electronic format, a template is available to assist you.  Under “Summary of the AOP”, under the “Graphical Representation” heading click on the link “Click to download template for graphical representation.” A Powerpoint template file should download via the default download mechanism for your browser. Click to open this file; it contains a Powerpoint template for an AOP diagram and instructions for editing and saving the diagram. Be sure to save the diagram as jpeg, jpg, gif, png, or bmp format. Once the diagram is edited to its final state, upload the image file as described above. More help

Authors

List the name and affiliation information of the individual(s)/organisation(s) that created/developed the AOP. In the context of the OECD AOP Development Workplan, this would typically be the individuals and organisation that submitted an AOP development proposal to the EAGMST. Significant contributors to the AOP should also be listed. A corresponding author with contact information may be provided here. This author does not need an account on the AOP-KB and can be distinct from the point of contact below. The list of authors will be included in any snapshot made from an AOP. More help

Point of Contact

Indicate the point of contact for the AOP-KB entry itself. This person is responsible for managing the AOP entry in the AOP-KB and controls write access to the page by defining the contributors as described below. Clicking on the name will allow any wiki user to correspond with the point of contact via the email address associated with their user profile in the AOP-KB. This person can be the same as the corresponding author listed in the authors section but isn’t required to be. In cases where the individuals are different, the corresponding author would be the appropriate person to contact for scientific issues whereas the point of contact would be the appropriate person to contact about technical issues with the AOP-KB entry itself. Corresponding authors and the point of contact are encouraged to monitor comments on their AOPs and develop or coordinate responses as appropriate.  More help
Jelle Broeders   (email point of contact)

Contributors

List user names of all  authors contributing to or revising pages in the AOP-KB that are linked to the AOP description. This information is mainly used to control write access to the AOP page and is controlled by the Point of Contact.  More help
  • Jelle Broeders
  • Marvin Martens

Status

The status section is used to provide AOP-KB users with information concerning how actively the AOP page is being developed, what type of use or input the authors feel comfortable with given the current level of development, and whether it is part of the OECD AOP Development Workplan and has been reviewed and/or endorsed. “Author Status” is an author defined field that is designated by selecting one of several options from a drop-down menu (Table 3). The “Author Status” field should be changed by the point of contact, as appropriate, as AOP development proceeds. See page 22 of the User Handbook for definitions of selection options. More help
Author status OECD status OECD project SAAOP status
Under development: Not open for comment. Do not cite
This AOP was last modified on June 04, 2021 15:05
The date the AOP was last modified is automatically tracked by the AOP-KB. The date modified field can be used to evaluate how actively the page is under development and how recently the version within the AOP-Wiki has been updated compared to any snapshots that were generated. More help

Revision dates for related pages

Page Revision Date/Time
CYP2E1 Activation April 09, 2018 11:02
Protein Adduct Formation March 26, 2018 09:45
Oxidative Stress in Brain April 04, 2018 14:24
Lipid Peroxidation April 04, 2018 14:33
Unfolded Protein Response March 07, 2019 09:47
General Apoptosis April 04, 2018 14:51
Neurodegeneration April 04, 2018 14:53
CYP2E1 Activation leads to Oxidative Stress in Brain April 05, 2018 03:40
Oxidative Stress in Brain leads to Lipid Peroxidation April 05, 2018 04:06
Lipid Peroxidation leads to Protein Adduct Formation April 05, 2018 04:18
Protein Adduct Formation leads to Unfolded Prortein Response April 05, 2018 04:25
Oxidative Stress in Brain leads to Unfolded Prortein Response April 05, 2018 04:37
Lipid Peroxidation leads to General Apoptosis April 05, 2018 04:48
Unfolded Prortein Response leads to General Apoptosis April 05, 2018 04:51
General Apoptosis leads to Neurodegeneration April 05, 2018 04:53
Acetaminophen November 29, 2016 18:42
Enflurane April 05, 2018 06:31
Halothane April 05, 2018 06:32
Isoflurane April 05, 2018 06:32
Methoxyflurane April 05, 2018 06:32
Sevoflurane April 05, 2018 06:33
Chemical:584015 (1-~13~C)Aniline April 05, 2018 06:33
Chlorzoxazone April 05, 2018 06:34
Titanium oxide (TiO) April 05, 2018 06:35
Isoniazid April 05, 2018 06:36
Ethanol April 05, 2018 06:38

Abstract

In the abstract section, authors should provide a concise and informative summation of the AOP under development that can stand-alone from the AOP page. Abstracts should typically be 200-400 words in length (similar to an abstract for a journal article). Suggested content for the abstract includes the following: The background/purpose for initiation of the AOP’s development (if there was a specific intent) A brief description of the MIE, AO, and/or major KEs that define the pathway A short summation of the overall WoE supporting the AOP and identification of major knowledge gaps (if any) If a brief statement about how the AOP may be applied (optional). The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance More help

The AOP has two different MIEs: protein adduct formation (MIEa) and CYP2E1 activation (MIEb). Protein adduct formation is the interaction between a chemical, or reactive metabolite, and a protein at molecular level. During this interaction a covalent bond is formed which occurs due to the reaction between an electrophilic chemical and the nucleophilic part of a protein. When a chemical forms a covalent bond with a protein the protein is damaged and can loses its function. Acetaldehyde, the metabolite of ethanol, is also one of these chemicals known to form protein adducts. This is why protein adduct formation is added in this AOP based on ethanol. CYP2E1 is one of the enzymes responsible for the metabolism of ethanol, and because of this metabolic activity the MIE in added in this AOP. CYP2E1 participates in the metabolism of endogenous, small and hydrophobic compounds using a oxidation reaction. CYP2E1 is mainly expressed in rat liver cells, but can also be found in rat brain cells. Furthermore, in the human brain CYP2E1 expression is mainly found in the amygdala and prefrontal cortex. At higher concentrations of ethanol the expression of CYP2E1 increases, as well as the activity of CYP2E1 since it has a relatively high Km value for ethanol. In this AOP four different KEs are used, which are oxidative stress (KE1), lipid peroxidation (KE2), unfolded protein response (UPR) (KE3) and apoptosis (KE4). Oxidative stress can be defined as the imbalance between ROS and defence mechanisms against these ROS. ROS levels in a cell can rise which leads to damage by the oxidizing free radicals. Lipid peroxidation is a form of direct damage to lipids in the cell membrane or organelle membranes. The cell membrane will eventually break due to the build-up of all the damage. MDA  and 4-hydroxynonenal (HNE) are two products of lipid peroxidation. UPR is a reaction activated by stress in the endoplasmic reticulum (ER). ER stress can be induced by too much protein folding which reaches a higher level than the folding capacity. Also accumulation of unfolded protein in the ER and protein adducts formation with important endoplasmic proteins can induce ER stress, which activates UPR. The final KE is apoptosis, which is programmed cell death in general. The process of apoptosis is well regulated and several signal proteins are known to induce the apoptotic process.

Background (optional)

This optional subsection should be used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development. The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. Examples of potential uses of the optional background section are listed on pages 24-25 of the User Handbook. More help

Summary of the AOP

This section is for information that describes the overall AOP. The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help

Events:

Molecular Initiating Events (MIE)
An MIE is a specialised KE that represents the beginning (point of interaction between a stressor and the biological system) of an AOP. More help
Key Events (KE)
This table summarises all of the KEs of the AOP. This table is populated in the AOP-Wiki as KEs are added to the AOP. Each table entry acts as a link to the individual KE description page.  More help
Adverse Outcomes (AO)
An AO is a specialised KE that represents the end (an adverse outcome of regulatory significance) of an AOP.  More help
Sequence Type Event ID Title Short name
1 MIE 1508 CYP2E1 Activation CYP2E1 Activation
2 MIE 1509 Protein Adduct Formation Protein Adduct Formation
3 KE 1510 Oxidative Stress in Brain Oxidative Stress in Brain
4 KE 1511 Lipid Peroxidation Lipid Peroxidation
5 KE 1512 Unfolded Protein Response Unfolded Prortein Response
6 KE 1513 General Apoptosis General Apoptosis
7 AO 1514 Neurodegeneration Neurodegeneration

Relationships Between Two Key Events (Including MIEs and AOs)

This table summarises all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP. Each table entry acts as a link to the individual KER description page.To add a key event relationship click on either Add relationship: events adjacent in sequence or Add relationship: events non-adjacent in sequence.For example, if the intended sequence of KEs for the AOP is [KE1 > KE2 > KE3 > KE4]; relationships between KE1 and KE2; KE2 and KE3; and KE3 and KE4 would be defined using the add relationship: events adjacent in sequence button.  Relationships between KE1 and KE3; KE2 and KE4; or KE1 and KE4, for example, should be created using the add relationship: events non-adjacent button. This helps to both organize the table with regard to which KERs define the main sequence of KEs and those that provide additional supporting evidence and aids computational analysis of AOP networks, where non-adjacent KERs can result in artifacts (see Villeneuve et al. 2018; DOI: 10.1002/etc.4124).After clicking either option, the user will be brought to a new page entitled ‘Add Relationship to AOP.’ To create a new relationship, select an upstream event and a downstream event from the drop down menus. The KER will automatically be designated as either adjacent or non-adjacent depending on the button selected. The fields “Evidence” and “Quantitative understanding” can be selected from the drop-down options at the time of creation of the relationship, or can be added later. See the Users Handbook, page 52 (Assess Evidence Supporting All KERs for guiding questions, etc.).  Click ‘Create [adjacent/non-adjacent] relationship.’  The new relationship should be listed on the AOP page under the heading “Relationships Between Two Key Events (Including MIEs and AOs)”. To edit a key event relationship, click ‘Edit’ next to the name of the relationship you wish to edit. The user will be directed to an Editing Relationship page where they can edit the Evidence, and Quantitative Understanding fields using the drop down menus. Once finished editing, click ‘Update [adjacent/non-adjacent] relationship’ to update these fields and return to the AOP page.To remove a key event relationship to an AOP page, under Summary of the AOP, next to “Relationships Between Two Key Events (Including MIEs and AOs)” click ‘Remove’ The relationship should no longer be listed on the AOP page under the heading “Relationships Between Two Key Events (Including MIEs and AOs)”. More help

Network View

The AOP-Wiki automatically generates a network view of the AOP. This network graphic is based on the information provided in the MIE, KEs, AO, KERs and WoE summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help

Stressors

The stressor field is a structured data field that can be used to annotate an AOP with standardised terms identifying stressors known to trigger the MIE/AOP. Most often these are chemical names selected from established chemical ontologies. However, depending on the information available, this could also refer to chemical categories (i.e., groups of chemicals with defined structural features known to trigger the MIE). It can also include non-chemical stressors such as genetic or environmental factors. Although AOPs themselves are not chemical or stressor-specific, linking to stressor terms known to be relevant to different AOPs can aid users in searching for AOPs that may be relevant to a given stressor. More help

Life Stage Applicability

Identify the life stage for which the KE is known to be applicable. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected. In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
human Homo sapiens NCBI

Sex Applicability

The authors must select from one of the following: Male, female, mixed, asexual, third gender, hermaphrodite, or unspecific. More help

Overall Assessment of the AOP

This section addresses the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and WoE for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). The goal of the overall assessment is to provide a high level synthesis and overview of the relative confidence in the AOP and where the significant gaps or weaknesses are (if they exist). Users or readers can drill down into the finer details captured in the KE and KER descriptions, and/or associated summary tables, as appropriate to their needs.Assessment of the AOP is organised into a number of steps. Guidance on pages 59-62 of the User Handbook is available to facilitate assignment of categories of high, moderate, or low confidence for each consideration. While it is not necessary to repeat lengthy text that appears elsewhere in the AOP description (or related KE and KER descriptions), a brief explanation or rationale for the selection of high, moderate, or low confidence should be made. More help

Domain of Applicability

The relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context are defined in this section. Biological domain of applicability is informed by the “Description” and “Biological Domain of Applicability” sections of each KE and KER description (see sections 2G and 3E for details). In essence the taxa/life-stage/sex applicability is defined based on the groups of organisms for which the measurements represented by the KEs can feasibly be measured and the functional and regulatory relationships represented by the KERs are operative.The relevant biological domain of applicability of the AOP as a whole will nearly always be defined based on the most narrowly restricted of its KEs and KERs. For example, if most of the KEs apply to either sex, but one is relevant to females only, the biological domain of applicability of the AOP as a whole would be limited to females. While much of the detail defining the domain of applicability may be found in the individual KE and KER descriptions, the rationale for defining the relevant biological domain of applicability of the overall AOP should be briefly summarised on the AOP page. More help

Essentiality of the Key Events

An important aspect of assessing an AOP is evaluating the essentiality of its KEs. The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence.The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs.When assembling the support for essentiality of the KEs, authors should organise relevant data in a tabular format. The objective is to summarise briefly the nature and numbers of investigations in which the essentiality of KEs has been experimentally explored either directly or indirectly. See pages 50-51 in the User Handbook for further definitions and clarifications.  More help

Key Event

Essentiality

MIEa (Protein Adduct Formation)

Moderate support. Activation of MIEa induces increased activation of KE 3, but direct evidence is not available. One theory about the mechanism is that adducts are formed with critical ER proteins. (Haberzettl, P. & Hill, B. G., 2013; Galligan, J. J. et al., 2014; Cumaoglu, A. et al., 2014; Kessova, I. G. & Cederbaum, A. I., 2005; Huličiak, M. et al., 2012; Sadrieh, N. & Thomas, P. E., 1994; Shin, N. Y. et al., 2007; Sapkota, M. & Wyatt, T. A., 2015; Tuma, D. J., 2002)

MIEb (CYP2E1 Activation)

High support. Direct evidence is available which prevents the upstream KE 1. CYP2E1 knockout as well as inhibition studies are performed. Activation of CYP2E1 by stressors also showed an increased. (Valencia-Olvera, A. C. et al., 2014; Haorah, J. et al, 2008; Luo, J., 2014; Yang, L. & Cederbaum, A., 2011; Lakshman, M. R. et al., 2013; Jimenez-Lopez, J. M. & Cederbaum, A. I., 2005; Gonzalez, F. J., 2005; Albano, E. et al., 1996; Albano, E., 2006; Wu, D. et al., 2012; Cederbaum, A. I., 2010; Lu, Y. et al., 2010; Oneta, C. M. et al., 2002; Lieber, C. S., 2004; Emerit, J. et al., 2004)

KE 1 (Oxidative Stress)

High support. Direct and indirect evidence is available for the essentiality of KE 1. Blocking ROS formation inhibits upstream KE 2 and KE 3. The indirect evidence showed that higher ROS induction showed an increased activity of upstream KE 2 and KE 3.

KE 2 (Lipid Peroxidation)

High support. There is much indirect evidence available showing that inducement of lipid peroxidation can increase activity of MIEb and KE 4. The direct evidence of blocking HNE which results in inhibition of upstream KE 4 shows that there is link between KE 2 and KE 4 and that the underlying molecular pathway is known.

KE 3 (UPR)

Moderate support. There is direct as well as indirect evidence available which shows molecular understanding of how KE 3 can induce KE 4. The uncertainty lies in whether ER stress alone can induce KE 4, or that KE 1 also plays a role in it. This is more discussed in detail in chapter 4.

KE 4 (Apoptosis)

High support. Neurodegeneration is the loss of neuron cells in the brain.

See table below where an overview is provided of the direct and indirect evidence. For the meaning of numbering see Abstract and the image of the AOP,

Key event relatio-nship

Methods

Influence on downstream Key events

Direct/Indirect evidence

KER 1: MIEb ---> KE1

1. Stimulation of CYP2E1 by stressors in rat livers.

2. Inhibition studies of CYP2E1 in neuron cells.

3. CYP2E1 KO in mice where TBARS values are measured.

4. Induction of CYP2E1 results in higher ROS levels an higher CYP2E1 expression, study performed in granule neuron cells.

1. Activation KE 1

2. Inhibition KE 1

3. Inhibition KE 1

4. Activation KE 1

1. Indirect

2. Direct

3. Direct

4. Indirect

KER 2: KE1 ---> KE2

1. Lower ROS level by adding higher concentrations of antioxidants or resveratrol (inhibitor of ROS). TBARS and LOOH product was measured in rat microsomes.

2. Correlation study where higher ROS levels increased lipid peroxidation in aging brains.

1. Inhibition KE 2

2. Activation KE 2

1. Direct

2. Indirect

KER 3: KE1 ---> KE3

1. Lower ROS levels by overexpression of antioxidant SOD1, NAC or GSH resulted in induction of UPR markers. Measured in neuron cells.

2. Stimulation of ROS formation by ethanol, which induces the UPR response in 2 hours after exposure.

1. Inhibition KE 3

2. Activation KE 3

1. Direct

2. Indirect

KER 4: KE2 ---> MIEa

1.Proteomic detection techniques for HNE adducts, HNE is a reactive aldehyde product of lipid peroxidation.

2. SERS monitoring detection, showed link between increased lipid peroxidation and increased protein adduct formation.

1. Activation MIEb

2. Activation MIEb

1. Indirect

2. Indirect

KER 5: MIEa ---> KE3

1. HNE (known to form protein adducts) treatment in rat aortic smooth muscle cells induced expression of the PERK pathway, which is part of the UPR. Same study is also performed in different settings.

2. Some toxicants can form protein adducts with ER proteins, what can induce ER stress and the UPR.

1. Activation KE 3

2. Activation KE 3

1. Indirect

2. Indirect

KER 6: KE2 ---> KE4

1. HNE can induce Fas/CD95DR expression, which regulated the extrinsic pathway of apoptosis.

2. Knockout of GSTA4 in mouse, which is an antioxidant for HNE, showed an increase in Fas expression.

3. ASK1 and JNK are activated by Fas. Increased HNE concentrations showed higher expression of ASK1 and JNK. When Fas was inhibited apoptosis was stopped.

4. HNE induces mitochondrial dysfunction which leads to apoptosis. Higher HNE levels showed increased expression of cytochrome c and caspases. Caspase 3 and 9 are mainly activated. Both are part of the intrinsic pathway of apoptosis.

1. Activation KE 4

2. Inhibition KE 4

3. Activation KE 4

4. Activation KE 4

1. Indirect

2. Direct

3. Indirect

4. Indirect

KER 7: KE3 ---> KE4

1. Higher expression of IRE1 and PERK, which are UPR markers, showed an increase of caspases expression. These caspases play a major role in the apoptotic pathway.

2. Inhibition of ER stress by DHCR24 resulted in a lower level of CHOP expression. Also an inhibition of apoptosis was shown.

1. Activation KE 4

2. Inhibition KE 4

1. Indirect

2. Direct

KER 8: KE4 ---> AO

1. Neuron loss is detected in neurodegenerative diseases, such as Alzheimer.

1. Activation AO

1. Indirect

Evidence Assessment

The biological plausibility, empirical support, and quantitative understanding from each KER in an AOP are assessed together.  Biological plausibility of each of the KERs in the AOP is the most influential consideration in assessing WoE or degree of confidence in an overall hypothesised AOP for potential regulatory application (Meek et al., 2014; 2014a). Empirical support entails consideration of experimental data in terms of the associations between KEs – namely dose-response concordance and temporal relationships between and across multiple KEs. It is examined most often in studies of dose-response/incidence and temporal relationships for stressors that impact the pathway. While less influential than biological plausibility of the KERs and essentiality of the KEs, empirical support can increase confidence in the relationships included in an AOP. For clarification on how to rate the given empirical support for a KER, as well as examples, see pages 53- 55 of the User Handbook.  More help

Quantitative Understanding

Some proof of concept examples to address the WoE considerations for AOPs quantitatively have recently been developed, based on the rank ordering of the relevant Bradford Hill considerations (i.e., biological plausibility, essentiality and empirical support) (Becker et al., 2017; Becker et al, 2015; Collier et al., 2016). Suggested quantitation of the various elements is expert derived, without collective consideration currently of appropriate reporting templates or formal expert engagement. Though not essential, developers may wish to assign comparative quantitative values to the extent of the supporting data based on the three critical Bradford Hill considerations for AOPs, as a basis to contribute to collective experience.Specific attention is also given to how precisely and accurately one can potentially predict an impact on KEdownstream based on some measurement of KEupstream. This is captured in the form of quantitative understanding calls for each KER. See pages 55-56 of the User Handbook for a review of quantitative understanding for KER's. More help

In AOP1 there are some knowledge gaps present which is one of the principles of the AOP concept. CYP2E1 activation is known to increase the ROS concentration in a cell, but the underlying mechanism is not completely understood. There are two main mechanisms which are suggested in literature, either CYP2E1 or NADPH oxidase could be the primary enzyme which is responsible for ROS formation and cause the further damage in the cells. NAPDH oxidase recycles the NADP+ which is formed during the reaction cycle of CYP2E1, during this cycle ROS is formed due to the uncoupling reaction. CYP2E1 shows a relatively high activity of NADPH oxidase activity and is poorly coupled with NADPH-cytochrome P450 reductase. When NADPH oxidase is inhibited by anti-CYP2E1 IgG a reduction of ROS induced lipid peroxidation was shown. Knock-out or inhibition of CYP2E1 itself resulted in lower oxidative stress. A study performed by Bradford et al. showed that NADPH oxidase knock-out mice attenuated liver injury, where CYP2E1 knock-out mice did not show attenuating of liver injury. On the other hand, NADHP oxidase knock-out mice did not reduce oxidative stress damage to DNA, where CYP2E1 knock-out mice did reduced the damage. Another study by Zhang et al. looked at the influence of NADPH oxidase, an inhibiter against NADPH oxidase was used which reduced the formation of ROS in PC12 cells. Finally, Shah et al. and Furukawa et al. also showed that NADPH oxidase inhibition leads to a reduced formation of ROS, both studies were done in different disease context. The principle of ROS formation by NADPH oxidase is the formation of H2O2 since O2 is used as a substrate. By the Fenton-Weiss-Haber reaction multiple oxidants can be produces. But as mentioned above, several studies showed that CYP2E1 inhibition alone is enough to reduce ROS formation. To take into account, studies described above are all done in liver cells. The mechanism of CYP2E1 activation could be different in the brain.

Another knowledge gap is the mechanism of protein adducts that can induce ER stress, and ultimately the UPR. The assumed mechanism is that protein adducts are formed with critical ER proteins, which leads to the dysfunction of the ER. Furthermore, it is also a possibility that protein adducts inhibit the folding of proteins. These proteins can accumulate in the ER and when the protein accumulation is higher than the capacity ER stress is induced. Further research must be done to define the mechanism of how ER stress is induced by protein adducts, which will eventually lead to the UPR.

Considerations for Potential Applications of the AOP (optional)

At their discretion, the developer may include in this section discussion of the potential applications of an AOP to support regulatory decision-making. This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. While it is challenging to foresee all potential regulatory application of AOPs and any application will ultimately lie within the purview of regulatory agencies, potential applications may be apparent as the AOP is being developed, particularly if it was initiated with a particular application in mind. This optional section is intended to provide the developer with an opportunity to suggest potential regulatory applications and describe his or her rationale.To edit the “Considerations for Potential Applications of the AOP” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Considerations for Potential Applications of the AOP” section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page or 'Update and continue' to continue editing AOP text sections.  The new text should appear under the “Considerations for Potential Applications of the AOP” section on the AOP page. More help

References

List the bibliographic references to original papers, books or other documents used to support the AOP. More help

Leist, M. et al. Adverse outcome pathways: opportunities, limitations and open questions. Arch. Toxicol. 204, 1–29 (2017).

LoPachin, R. M. & DeCaprio, A. P. Protein adduct formation as a molecular mechanism in neurotoxicity. Toxicological Sciences 86, 214–225 (2005).

Cederbaum, A. I. Alcohol Metabolism. Clinics in Liver Disease 16, 667–685 (2012).

Sapkota, M. & Wyatt, T. A. Alcohol, aldehydes, adducts and airways. Biomolecules 5, 2987–3008 (2015).

Tuma, D. J. Role of malondialdehyde-acetaldehyde adducts in liver injury. Free Radical Biology and Medicine 32, 303–308 (2002).

Neafsey, P. et al. Genetic polymorphism in CYP2E1: Population distribution of CYP2E1 activity. Journal of Toxicology and Environmental Health - Part B: Critical Reviews 12, 362–388 (2009).

Zimatkin, S. M., Pronko, S. P., Vasiliou, V., Gonzalez, F. J. & Deitrich, R. A. Enzymatic mechanisms of ethanol oxidation in the brain. Alcohol. Clin. Exp. Res. 30, 1500–1505 (2006).

Toselli, F. et al. Expression of CYP2E1 and CYP2U1 proteins in amygdala and prefrontal cortex: Influence of alcoholism and smoking. Alcohol. Clin. Exp. Res. 39, 790–797 (2015).

Zakhari, S. Alcohol metabolism and epigenetics changes. Alcohol Res. 35, 6–16 (2013).

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